1. Field of the Invention
This invention relates to an exposure apparatus used in the lithography process for manufacturing, for example, semiconductor devices, liquid crystal display devices, thin film magnetic heads or the like, and particularly to a scanning exposure apparatus in which a mask (or a reticle) and a photosensitive substrate are moved in synchronisn with each other to thereby expose the pattern of the mask on the photosensitive substrate.
2. Related Background Art
Now, in the photolithography process for the manufacture of semiconductor devices, use is made of a projection exposure apparatus in which the pattern of a mask or a reticle (hereinafter generically referred to as the reticle) is transferred onto a semiconductor wafer having a photosensitive material (photoresist) applied thereto through a projection optical system. Recently, in order to meet the tendency of semiconductor devices toward bulkiness and minuteness, it has been desired to accomplish the enlargement of the image field of the projection optical system and an improvement in resolution. However, it is very difficult in design and manufacture to realize both of the higher resolution and wider field of the projection optical system. So, attention has been paid to a scanning type exposure apparatus in which, as disclosed, for example, in U.S. Pat. Nos. 4,747,678, 4,924,257 and 5,194,893, only a localized area on a reticle is illuminated and the reticle and a wafer are moved in synchronism with each other to thereby transfer the pattern of the reticle onto the wafer. The scanning type exposure apparatus, even if the image field of the projection optical system thereof is small, can transfer a pattern image of a large area onto the wafer and moreover can improve the resolution of the projection optical system relatively easily.
Now, in the scanning type exposure apparatus, the reticle is scanned relative to an illumination area defined by a field stop (reticle blind). Accordingly, during the start and termination of the scanning, even the outside of the pattern area on the reticle is illuminated and therefore, an unnecessary pattern may be transferred onto the wafer. To prevent the transfer of the unnecessary pattern, it would occur to mind to increase the width of a light intercepting zone which defines the pattern area, but in such case, the area of the pattern area on the reticle would become small, and this is against the desire to make the area of the transfer pattern large. Also, in a case where only one of two circuit patterns on the reticle is scanned and exposed on the wafer, a part of the other circuit pattern will be transferred onto the wafer if the width of a light intercepting zone partitioning the two circuit patterns is smaller than the width of the illumination area.
So, for example, in Japanese Patent Application Laid-Open No. 4-196513 (U.S. Ser. No. 068,101 filed on May 28, 1993), it is proposed to make each blade (light intercepting plate) of a field stop defining an illumination area on a reticle movable, drive the blades at the start and end of scanning and vary the rectangular aperture in the field stop, i.e., the width of the illumination area on the reticle in the scanning direction, thereby preventing an unnecessary pattern from being illuminated. However, in the scanning type exposure apparatus, to obtain good illuminance uniformity on the wafer (in other words, to effect highly accurate control of exposure amount), the width of the illumination area in the scanning direction must be uniform. Accordingly, it is required of the field stop that there be little unevenness in edge portions perpendicular to the scanning direction and that the two edge portions be movement-controlled while being kept sufficiently parallel to each other when the width in the scanning direction is varied. However, the edge portions of the field stop are formed by something like mechanical knife edges. That is, mechanical knife edges have the inconvenience that the shape error thereof is great and the uniformity of illuminance is reduced. Also, in movement-controlling the aforedescribed field stop in synchronism with the scanning of the reticle, it is difficult to satisfy the accuracy required of parallelism. To satisfy this, a highly accurate positioning mechanism will become necessary, and this leads to the inconvenience that the varying mechanism will become very much complicated.
Also, in a scanning type exposure apparatus using a pulse light source, it is proposed to make the intensity of light on a wafer in the scanning direction into a substantially isosceles trapezoidal shape as disclosed, for example, in U.S. Pat. No. 4,822,975, in order to reduce the irregularity of the exposure amount on the wafer.
It is the object of the present invention to provide a scanning type exposure apparatus in which good illuminance uniformity (exposure amount control accuracy) is obtained and which can transfer only a desired pattern on a mask onto a photosensitive substrate.
A first scanning type exposure apparatus according to the present invention has a light source generating illuminating light, an illuminating optical system for illuminating an illumination area on a mask by the illuminating light, and a projection optical system for projecting the image of a pattern in the illumination area onto a substrate, and the mask is scanned in a predetermined direction relative to the illumination area and the substrate is scanned in a predetermined direction relative to an exposure area conjugate with the illumination area with respect to the projection optical system, whereby the image of the pattern of the mask is scanned and exposed on the substrate. A fixed field stop for setting the illumination area on the mask to a predetermined shape and a predetermined size, and a light intercepting member for variably limiting the range of the illuminated area set on the mask by the field stop with respect to the predetermined direction are disposed on or near a plane in the illuminating optical system which is conjugate with the pattern surface of the mask. Also, the shape of the illumination area set on the mask by the field stop may preferably be set to a shape conforming to an integrated exposure amount distribution with respect to a direction perpendicular to the predetermined direction on the substrate. Further, it is preferable that the field stop be formed by coating the light-transmitting substrate with light intercepting film and the surface coated with the light intercepting film be installed at a position defocused by a predetermined amount from the plane conjugate with the pattern surface of the mask.
According to the first scanning type exposure apparatus of the present invention, immediately after the start, and immediately before the termination, of the synchronized scanning of the mask and the substrate, a part of the illumination area set on the mask by the fixed field stop protrudes outwardly of a light intercepting zone on the mask which defines the pattern area. So, the light intercepting member provided discretely from the fixed field stop is moved in synchronism with the scanning of the mask, whereby the edge portion of the projected image of the light intercepting member onto the mask is set in the light intercepting zone of the mask. Thereby, a void pattern outside the light intercepting zone is prevented from being exposed on the substrate, in other words, a part thereof is prevented from being sensitized by light passing the outside of the light intercepting zone onto the substrate. Also, when the whole of the illumination area is present in the pattern area on the mask, the illumination area has its shape and size set by the fixed field stop. Accordingly, the position control accuracy of the light intercepting member may be approximately the width of the light intercepting zone on the mask. As described above, the fixed field stop for determining the integrated exposure amount on the substrate and the light intercepting member for limiting the illumination area on the mask are disposed separately from each other and therefore, the positioning accuracy of the light intercepting member may be rougher than in the apparatus of the conventional follow-up type, and the structure of a moving mechanism therefore and a control system can be simplified and the set accuracy of the shape and size of the illuminated area by the fixed field stop can be made higher.
Also, where the shape of the aperture in the field stop is rectangular, if scanning exposure is effected with the mask and the substrate moved in Y-direction, the distribution of the integrated exposure amount E(X) on the substrate with respect to the non-scanning direction (X-direction) perpendicular to the scanning direction (Y-direction) may sometimes be not uniform as shown in FIG. 5C of the accompanying drawings. So, as shown, for example, in FIG. 6A of the accompanying drawings, the shape of the aperture in the field stop is modified in conformity with the integrated exposure amount E(X) of FIG. 5C. Thereby, the distribution of the integrated exposure amount E(X) on the substrate in the non-scanning direction can be uniformized.
Further, where the fixed field stop is formed by coating the light transmitting substrate within the predetermined range thereof with light intercepting film, the aperture as shown, for example, in FIG. 6A can be formed highly accurately and the irregularity of the integrated exposure amount becomes small. Also, where the surface coated with the light intercepting film is installed at a position defocused by a predetermined amount from a plane conjugate with the pattern surface of the mask, the image of a foreign substance (dust or the like) adhering to the light transmitting substrate is blurredly projected onto the substrate and therefore, the foreign substance does not affect the irregularity of the integrated exposure amount on the substrate.
A second scanning type exposure apparatus according to the present invention is provided with an illuminating optical system for illuminating an illumination area on a mask, and a relative scanning member for scanning the mask and a photosensitive substrate in synchronism with each other, and has a fixed field stop disposed on a first mounting surface of a group of mounting surfaces comprising a surface near the pattern-formed surface of the mask, a surface in the illuminating optical system which is conjugate with the pattern-formed surface and a surface near the conjugate surface for setting the width of the illumination area on the mask in the scanning direction. The second apparatus is further provided with a movable field stop disposed on a second mounting surface differing from the first mounting surface of the group of mounting surfaces for setting a variable exposure area to be actually exposed on the photosensitive substrate in the illumination area on the mask, the movable field stop has a first vane and a second vane for setting fore and rear edge portions, respectively, relative to the scanning direction of the exposure area, and at the start of the exposure of the pattern of the mask, the first vane of the movable field stop is driven to move the fore edge portion relative to the scanning direction of the exposure area in synchronism in the scanning direction relative to the illumination area, and at the end of the exposure of the pattern of the mask, the second vane of the movable field stop is driven to move the rear edge portion relative to the scanning direction of the exposure area in synchronism in the scanning direction relative to the illumination area.
A third scanning type exposure apparatus according to the present invention is provided with a light source generating illuminating light, an illuminating optical system for illuminating an illumination area on a mask by the illuminating light, a projection optical system for projecting the image of a pattern in the illumination area onto a photosensitive substrate, and a relative scanning member for scanning the mask and the photosensitive substrate in synchronism with each other relative to the illumination area, and has a fixed field stop disposed on a first mounting surface spaced apart by xcex94z in the direction of the optical axis thereof from a surface conjugate with the pattern-formed surface of the mask for setting the width of the illumination area on the mask in the scanning direction. The third apparatus is further provided with a movable field stop disposed on a second mounting surface substantially coincident with the surface conjugate with the pattern-formed surface of the mask for setting a variable exposure area to be actually exposed on the photosensitive substrate in the illumination area on the mask, and when the numerical aperture of the photosensitive substrate side of the projection optical system is NAW and the coherence factor of the illuminating light from the illuminating optical system is "sgr" and the projection magnification of the projection optical system is MRW and the magnification of the optical system between the surface conjugate with the pattern-formed surface of the mask near the first mounting surface and the pattern-formed surface is MBR and the allowable minimum value of the radius of the blur, on the photosensitive substrate, of the light emitted from a point on the surface on which the fixed field stop is disposed is xcex94Dmin, xcex94z which is the defocus amount of the first mounting surface, the following condition is satisfied:
|xcex94z|xe2x89xa7xcex94Dmin/[MBRxc2x7MRWxc2x7tan{arc sin(MBRxc2x7MRWxc2x7NAWxc2x7"sgr")}]xe2x80x83xe2x80x83(1)
According to the second scanning type exposure apparatus, the field stop for determining the width of the illumination area in the scanning direction is fixed and therefore, manufacture or adjustment can be done precisely so that the edge portions in the scanning direction may become sufficiently parallel to each other. Also, provision is made of the movable field stop having the first vane and the second vane for determining the variable exposure area which may be rougher in shape accuracy than the illumination area. So, when for example, only one of a plurality of pattern areas on the mask is to be transferred onto the photosensitive substrate, the first vane is driven at the start of scanning exposure to move the fore edge portion of the exposure area relative to the scanning direction in the scanning direction relative to the illumination area, and at the end of scanning exposure, the second vane is driven to move the rear edge portion of the exposure area in the scanning direction relative to the illumination area.
Thereby, only a desired pattern area is transferred onto the photosensitive substrate. In this case, the interval between the first vane and the second vane may be, at greatest, of such a degree that it slightly exceeds the width of the area conjugate with the illumination area. Moreover, the movement strokes of the first and second vanes may be of such a degree that slightly exceeds the width of the area conjugate with the illumination area. Therefore, the movable field stop may be small. Further, the width of the light intercepting portion which partitions the plurality of pattern areas on the mask can be made smaller than the width of the illumination area in the scanning direction, and the area of the pattern areas on the mask can be secured widely. Also, the fixed field stop can be disposed in deviated relationship with the surface conjugate with the pattern-formed surface of the mask and therefore, spatial compatibility can be obtained even when the movable field stop for determining the variable exposure area is disposed, for example, on a plane substantially conjugate with the pattern-formed surface of the mask.
Also, according to the third scanning type exposure apparatus of the present invention, use is made of the fixed field stop and therefore, manufacture or adjustment can be done precisely so that the edge portions of the slit-shaped illumination area in the scanning direction may become sufficiently parallel to each other. Further, use is also made of the movable field stop and therefore, only a desired circuit pattern can be transferred onto the photosensitive substrate even when the width of the light intercepting portion which partitions a plurality of circuit patterns on the mask is small. Also, the movable field stop is disposed on a plane substantially conjugate with the pattern-formed surface of the mask, and the fixed field stop is disposed while being deviated from the conjugate plane by the interval xcex94z which satisfies the aforementioned conditional expression (1). Therefore, as shown in FIG. 6B of the accompanying drawings, predetermined slopes can be given to the both ends of the illuminance distribution of the illumination area in the scanning direction. This is convenient in controlling the exposure amount and in maintaining the uniformity of illuminance when the exposure light source is particularly a pulse light source such as an excimer laser.